diff --git a/.github/workflows/guix.yml b/.github/workflows/guix.yml
index c826cd334..fdbfe0175 100644
--- a/.github/workflows/guix.yml
+++ b/.github/workflows/guix.yml
@@ -71,7 +71,7 @@ jobs:
       - name: purge apparmor
         run: sudo apt purge apparmor
       - name: build
-        run: SUBSTITUTE_URLS='http://bordeaux.guix.gnu.org' HOSTS="${{ matrix.toolchain.target }}" ./contrib/guix/guix-build
+        run: ADDITIONAL_GUIX_TIMEMACHINE_FLAGS="--disable-authentication" SUBSTITUTE_URLS='http://bordeaux.guix.gnu.org' HOSTS="${{ matrix.toolchain.target }}" ./contrib/guix/guix-build
       - uses: actions/upload-artifact@v4
         with:
           name: ${{ matrix.toolchain.target }}
diff --git a/contrib/guix/libexec/build.sh b/contrib/guix/libexec/build.sh
index 5f85671ac..7d17de312 100644
--- a/contrib/guix/libexec/build.sh
+++ b/contrib/guix/libexec/build.sh
@@ -77,6 +77,7 @@ store_path() {
 # includes/libs
 NATIVE_GCC="$(store_path gcc-toolchain)"
 NATIVE_GCC_STATIC="$(store_path gcc-toolchain static)"
+RUST_SRC="$(store_path rust rust-src)/lib/rustlib/src/rust"
 
 unset LIBRARY_PATH
 unset CPATH
@@ -310,7 +311,8 @@ mkdir -p "$DISTSRC"
       -DCMAKE_SHARED_LINKER_FLAGS="${HOST_LDFLAGS}" \
       -DCMAKE_SKIP_RPATH=ON \
       -DMANUAL_SUBMODULES=1 \
-      -DGUIX=1
+      -DGUIX=1 \
+      -DRUST_SRC=${RUST_SRC}
 
     make -C build --jobs="$JOBS"
 
diff --git a/src/fcmp_pp/fcmp_pp_rust/CMakeLists.txt b/src/fcmp_pp/fcmp_pp_rust/CMakeLists.txt
index 91f53b4ad..69046d07f 100644
--- a/src/fcmp_pp/fcmp_pp_rust/CMakeLists.txt
+++ b/src/fcmp_pp/fcmp_pp_rust/CMakeLists.txt
@@ -86,13 +86,13 @@ endif()
 set(RUST_TARGET "${RUST_ARCH}-${RUST_PLATFORM}${RUST_TOOLCHAIN}")
 
 if (GUIX)
-  set(CARGO_CMD __CARGO_TESTS_ONLY_SRC_ROOT=/gnu/store/aymb9k11rmmkizvg8qcjqv57vx2mvkxn-rust-1.77.1-rust-src/lib/rustlib/src/rust RUSTFLAGS=-Cpanic=abort RUSTC_BOOTSTRAP=1 cargo build --release --target "${RUST_TARGET}" -Zbuild-std=std,panic_abort --no-default-features)
+  set(CARGO_CMD __CARGO_TESTS_ONLY_SRC_ROOT=${RUST_SRC} RUSTFLAGS=-Cpanic=abort RUSTC_BOOTSTRAP=1 cargo build --release --target "${RUST_TARGET}" -Zbuild-std=std,panic_abort --no-default-features)
   set(TARGET_DIR "release")
 else ()
   if (CMAKE_BUILD_TYPE STREQUAL "Debug")
     set(CARGO_CMD cargo build --target "${RUST_TARGET}")
     set(TARGET_DIR "debug")
-  elseif ()
+  else ()
     set(CARGO_CMD cargo build --target "${RUST_TARGET}" --release)
     set(TARGET_DIR "release")
   endif ()